1. Field of the Invention
The present invention relates to a power source unit including a main power source, mainly employing an AC/DC converter, and an auxiliary power source which can store energy. The present invention can be employed for apparatuses such as image forming apparatuses including copiers, printers, facsimile machines or the like, which devices may exhibit greater fluctuation in power consumption, with low power consumption mode set during a waiting condition, a high power consumption mode is set when the device is activated for printing, and a medium power consumption mode is set when activation is completed and operation can commence.
2. Description of the Background Art
Recently, environmental concerns have become important matters, in which energy saving is one of important issue. To implement energy saving, many functions of electronic devices are set in a deactivated condition during a standby mode when the devices are not in use except for a receiving function which is used for waiting for operational instructions signals. Such a condition, in which many functional units are deactivated, may be referred to in general as an energy saving mode or a sleep mode. For example, when a printer enters the energy save mode, power supply to a fusing unit, a drive motor, or the like is stopped, whereas power is supplied only to an electronic circuit and functional elements used to receive signals, including printing instructions.
Power consumption of electronic circuits in the waiting condition (or load power during the energy saving mode) is very small compared to power consumption of functional units used for printing operation, such as a fusing unit, a motor driver, or the like. Power consumption during the energy save mode has some international official standards such as Energy Star, which sets a standard measurement method for power consumption. Because such standard can be used to compare power consumption of different devices of different manufacturers, users can use such standard as one of decision making tools when selecting devices.
Further, for example, image forming apparatuses using an electrophotographic process, such as copiers, printers, facsimile machines, and multi-functional peripherals combining various functions, have become more sophisticated and can now perform many functions. As a result, the structures of these image forming apparatuses has become more complex, thereby increasing maximum power consumption of the image forming apparatuses. Further, there is a trend to increase power supply to a fusing heater to reduce a waiting time of an operator caused by of the image forming apparatus itself, such as a waiting time for starting up the fusing unit and suspension of operation during printing or copying due to a decrease of fusing temperature. Because conventional power source lines (e.g., commercial alternating current power source) have a given upper limit for supplyable power, an auxiliary power source may be used with a main power source to cope with such power supply increase. Thus, for example, when a power amount required to be supplied by the main power source is smaller than a predetermined value, an auxiliary power source is charged and power is stored in the auxiliary power source. Conversely, when power greater than the predetermined value of the commercial alternating current power source is required to be supplied, the power stored in the auxiliary power source is supplied, by which a power supply that can change rapidly within a relatively short time can be effectively supplied.
A main power source used for supplying power to a direct current (DC)-using load device may be an AC/DC converter having a switching power source. Because the switching power source is designed in a way that AC/DC conversion efficiency becomes maximum under a normal rating load condition, the AC/DC conversion efficiency decreases under a low (or light) load condition such as at a waiting condition. Thus, for example, with some typical switching power sources, AC/DC conversion efficiency is 80% under a normal rating load condition, but only 20% under a low (or light) load condition such as at a waiting condition. Accordingly, to achieve energy saving, an improvement of AC/DC conversion efficiency under the low (or light) load condition becomes an important technical consideration.
In JP-2000-184716-A (reference 1), to reduce power consumption of an infrared light receiving circuit of home electric appliance such as television set, which receive operation signal(s) from a remote controller during the waiting condition, a charge storing unit may be disposed in addition to an AC/DC converter, and if voltage decreases, a power source unit drives the AC/DC converter to charge the charge storing unit.
In a power source unit of JP-2004-74558-A (reference 2), an auxiliary power source is charged by a main power source when the main power source outputs power with a high efficiency output such as when a greater power is output, and when the main power source outputs a smaller power with a low efficiency output to supply power under a low (or light) load condition (or energy save mode), the main power source is set to OFF, and the auxiliary power source supplies power to a load device.
In an image forming apparatus of JP-2005-27374-A (reference 3), a direct current main power source such as AC/DC converter charges a storing unit, and the storing unit supplies micro power to a memory backup function, a signal reception/detection function, or the like. When power stored in the storing unit becomes smaller, a switching unit is used to switch condition of the storing unit from discharging to charging.
In JP-2004-266984-A (reference 4), a AC/DC converter (direct current power source unit) used as a switching power source, and an auxiliary power source chargeable by a circuit different from the power source unit (i.e., AC/DC converter) are included, and power source unit switches power supply to an energy saving load device.
In a power source unit of JP-2007-127843-A (reference 5), a fusing heater needs a higher power consumption, and an AC/DC converter, which supplies power to other DC-using load devices, may also need a higher power consumption. When combined power supply for the fusing heater and AC/DC converter exceeds an upper limit of commercial alternating current power, the AC/DC converter is set to OFF to reduce commercial alternating current load, and an auxiliary power source supplies power to DC-using load devices.
However, the auxiliary power sources for the power source units disclosed in the references 1 to 4 supply power only to an energy saving load device, which consumes a little power. Accordingly, a load power cannot be increased more than an upper limit of commercial alternating current used as an initial power source. The power source unit of reference 5 (JP-2007-127843-A), can increase load power more than an upper limit of commercial alternating current, but a power output efficiency under a low (or light) load condition such as a waiting condition becomes low.